As means for improving properties and, specifically, gas barrier properties of various kinds of plastic base materials, there has been known an art of forming an inorganic barrier layer comprising a silicon oxide or the like by vacuum evaporation on the surface of the plastic base material (patent document 1).
In a variety of electronic devices that are developed and put to practical use in recent years, such as organic electroluminescent devices (organic EL devices), solar cells, touch panels, and e-papers, it is a requirement to avoid the leakage of the electric charge. Therefore, a high water barrier property has been desired for the plastic base materials that form circuit boards or for the plastic base materials such as films for sealing the circuit boards. The above-mentioned inorganic barrier layer, however, is not capable of meeting the requirement of water barrier property of such a high degree. Therefore, there have been made a variety of proposals in an effort to improve the water barrier property.
A patent document 2, for instance, is proposing a gas barrier laminate comprising a plastic base material, an inorganic barrier layer formed on the surface of the plastic base material, and, on the inorganic barrier layer, a sealing layer in which nano particles such as of a metal oxide and carbon nano tubes are dispersed as hygroscopic agents.
A patent document 3 proposes a gas barrier laminate (film) comprising an inorganic barrier layer, an organic layer and a water-trapping layer that are formed on a base film, the water-trapping layer being formed of a hygroscopic polymer (concretely, a polyamide) or being formed by dispersing a hygroscopic material such as silica gel or aluminum oxide in a high molecular binder such as electron ray-curable or ultraviolet ray-curable resin.
Further, a patent document 4 proposes a gas barrier laminate comprising a plastic base material, a gas barrier layer vapor-deposited on the surface of the plastic base material, and a hygroscopic layer formed thereon, the hygroscopic layer containing an alkylene oxide, acrylate nano particles or an organometal complex.
Even with the gas barrier laminates proposed in these patent documents 2 to 4, however, it is difficult to attain a high degree of water barrier property. For example, to attain such a super water barrier property that the water vapor permeability is not more than 10−6 g/m2/day, it becomes necessary to employ a layer structure that includes many layers for adsorbing moisture (hygroscopic layers or sealing layers) requiring increased laborious work for forming the multilayer structure and, therefore, causing a decrease in the productivity. Therefore, it has been desired to further improve the water barrier property. Upon absorbing water, further, the layer for adsorbing moisture (hygroscopic layer or sealing layer) swells and lacks dimensional stability.